Electrical earth borehole logging is well known and various devices and various techniques have been described for this purpose. Broadly speaking, there are two categories of electrical logging devices. In the first category, a transmitter (such as a current electrode) is used in conjunction with a diffuse return electrode (such as the tool body). A measured electric current flows in a circuit that connects a current source to the transmitter, through the earth formation to the return electrode and back to the current source in the tool. In inductive measuring tools, an antenna within the measuring instrument induces a current flow within the earth formation. The magnitude of the induced current is detected using either the same antenna or a separate receiver antenna. The present disclosure belongs to the first category.
With tools in the first category, the electrode mandrel sensors are often non-serviceable in the field, since electrodes may not be removed/installed without compromising the fluid seal between the interior and exterior of the logging device. This disclosure addresses these and other problems.